I doubt barrel length adds much. A full choke adds maybe 30 fps, random variation between barrels adds or subtracts some as well. Factory speeds vary a lot. All in all, it's just an estimate. 1180 sounds fine.

Here's a paragraph from my tests:

The most open choke, cylinder, was tested at the start and end of the experiment and recorded speeds of 1154 and 1159 fps. The modified choke produced a speed of 1162 fps.

There were 5 full-choke “trap” barrels with bores ranging from 0.727 to 0.733 inches. They produced speeds from 1179 to 1188 fps. Two more with magnum chambers also fell within that range. A single 34-inch trap barrel clocked 1201 fps.

It has a bit to do with the equipment used to measure velocity. The units the factory uses for pressure and velocity testing work slightly different from the optical sensor consumer units. The consumer units seem to read a little higher. A tighter choke seems to add velocity and barrel length has a slight effect. Neil Has the right idea and his results are similar to what I have found. I have tested factory rounds and compared them to my reloads and I'm confident that they are right where they should be. I have also seen a wide variation in some factory shells.

I agree with Neil and Quack Shot, but would add an exception. My limited testing on one brand of imported discount shell suggests that the velocity printed on the box is actually about 50 ft/sec higher than the actual velocity as measured with an induction chronograph.

But, when I tested another brand, made by the same factory, I got unusual results. One box was labeled 2 3/4 dram (1140 ft/sec) and another box was labeled 3 dram (1200 ft/sec) and both boxes gave nearly identical velocities when tested (1161-1174 ft/sec). I suspect that the factory simply put the same shell in differently labeled boxes.

We checked 6 new shells and 20 reloads w/ 5 shot tests. I was most surprised with the Federal new loads. The Plastic Handicap averaged 1,313 fps w/ a 34" barrel. The 3 dram averaged 1,247 fps out of a 34" barrel and 1,226 fps out of a 32". The Win Superhandicap averaged 1,250 fps out of a 32" barrel.
These were chrono'd in March of 2001. Add 10 fps per 1" of barrel length. I'd be glad to send the data to anyone. Our reloads were with Promo,Red Dot, and Int.Clays using Fed, Rem, and Win hulls, and 3 different primers and wads.

My testing over several years has proven that there are several issues when using the home-owner type chronographs, even the expensive ones. Length of barrel, temperature, choke, and distance from the first or start sensor will all have "some" affect. Some are not particularly remarkable alone but when considering the entire situation on any given day or circumstance can make a considerable difference. Without getting even a little exact, I'll just repeat what Oehler says in their instructions for my model 35P chronograph and that is that when testing shot shells, we should reduce the readings buy as much as 3% and we should use the most open choke available, preferably cylinder bore.

The length of barrel may not be too remarkable when only an inch difference is involved but when testing with a 26" skeet barrel vs. a 34" single trap barrel the difference is obvious. Add to that if using a fixed skeet choke on the short barrel and fixed full choke on the long one, and the difference will be quite remarkable. When using the home chrono, the tester should always have a way to measure the distance the muzzle is from the first or start sensor to ensure all testing is from the same distance and that distance should be far enough back so as to not cause errors from muzzle blast. I am fortunate to have a M.32 O/U with a 28" barrel and using skeet choke tubes can almost always come very close to matching velocities printed on factory boxes with it on a day with 70 to 90* temps. So I use that as my standard test gun and believe the results do have a degree of reliability.

More recently, however, I've taken to making this suggestion. If you see a shell you'd like to match but don't want to bother with different guns, barrels, chokes et cetera then take the gun you'll use in competition and test them on the chronograph. Don't concern yourself with accuracy to what's printed on boxes but then build a reload that matches the previous test through your gun, your barrel, your preferred choke and at a typical day's temperature.....breakemall.....Bob Dodd

I believe I have also encountered the same "Bargain" loads as you had observed. I also checked the shot from a few sample shells and they were within a few thousandths, on the average, but they were marked as two different sizes on the box and the shells. I also found some very poor cold weather performance out of these loads. There were a few other bargain shells that had issues, but this one manufacturer was memorable. I also had the basewads migrating up into the hull after firing. I never had one exit the hull, but they did come loose and move forward. I never bought any more of these and will not shoot them in my guns or reload the hulls. There are a lot of people using them, but I'm not one of them.

It appears that there is a slight difference from a longer barrel, but I have seen just the opposite, so it's not always valid. When I have a valid average for comparison, I had a 26" Skeet Barrel vs a 30" Trap barrel. The chokes were similar. For the six loads I tested, the average difference was about 30-35 fps higher in the Trap barrel. One load was a bit higher than that, having about a 60 fps gain in the longer barrel. It was a load using a slower powder. It was not a target load. I have seen higher gains from using a tighter choke, but I try using the most open choke I have available when testing for velocity. I had a comparison between a Factory Target barrel in an 1100 Classic trap vs a Hastings bareel in the same gun. With a slightly tighter choke, the hastings barrel was a good 55 fps faster using the same loads.

timb99 much of what Quacker says would mirror my recollections. I don't have data to quote on the situations I encountered because I never figured it would be something I'd be sharing. I seem to recall using different guns and different barrel lengths could and some did result in differences in the 30 to 50fps area. And, I've read the same stuff regarding the all-the-powder-is-burned statement. As I've suggested, I generally, now, recommend just using your gun, your barrel, your chosen choke to measure some known factory shell and then just match that result with your preferred components.....Bob Dodd